This invention relates to catheterization practice, and more particularly to means by which a sheath through which a catheter is passed may be controllably sealed.
Catheterization, as that term is used herein, implies the passage of an elongate, usually hollow member, into and along vessels of the cardiovascular system. Catheters are widely employed in measurement of vascular pressures, angiography, blood gas determinations, indicator dilution studies and the like. Percutaneous techniques of catheter placement have become increasingly popular, replacing to a significant extent procedures requiring exposure of the vessel by surgical cutdown. In the so-called "Seldinger" percutaneous technique, the vessel wall and overlying tissue is pierced with a hollow needle through which a flexible wire is passed into the vessel. The needle is withdrawn over the extracorporeal end of the wire, which is then used to guide a relatively stiff catheter introducer or vessel dilator bearing a catheter sheath into the vessel. Once the sheath is in place, both introducer and wire are withdrawn, and the extracorporeal or distal end of the sheath is sealed, as with a luer lock seal, pending introduction of a catheter through the sheath. This technique has proved generally satisfactory for venous catheterizations, notwithstanding the fact that when a catheter is passed through the distal end of the sheath a leak path invariably is created along the sheath-catheter interface, owing to the relatively low vascular pressures encountered in such catheterizations. To the extent they permitted introduction of anticoagulants such as heparin only at the proximal end of the catheter, catheterization techniques heretofore in use were more likely subject to coltting adjacent the point of catheter entry. Again, such clotting is of but minor concern in venous catheterization, since transmigrating clots tend to be filtered in the lungs without any adverse effect. But in arterial catheterization, uncontrolled clotting can lead to major vascular and coronary occlusions. For that reason and because of the great vascular pressures which are exerted along the sheath-catheter interface with the concomitant risk of substantial blood loss, arterial catheterization has until now been less widely practiced and more commonly problematic than venous catherization. In view of the importance of the former in, e.g., aortic arch and branch radiography, renal studies, studies of the left heart and of the vascular anatomy of the brain, it is apparent that a need exists for improved catheter sheath sealing means, and particularly for such means safely suited to arterial catheterization techniques.